Moving from principles to action for energy supply that mitigates
against climate change requires a long-term perspective. Energy
infrastructure takes time to build up; new energy technologies take
time to develop. Policy shifts often also need many years to take
effect. In most world regions the transformation from fossil to
renewable energies will require additional investment and higher
supply costs over about twenty years

CO2 emissions by source

In 2050, coal will be by far the largest source of CO2, mainly from coal-fired power stations in China and India as well as power stations in other developing countries. Since those emissions are mainly from power stations built between 2000 and 2015, and the average lifetime of a coal-fired power plant is calculated at 40 years, in order to achieve the projected reduction, the construction of new coal power stations must end across most of the world by 2015 and in developing countries by 2020.

The second biggest emitter is oil, mainly from the remaining oil used in the transport sector.